Converter station and a method for control thereof

Abstract

A converter station an element adapted to determine a value of an actual temperature of any critical component of the station and an element adapted to determine a value of an actual temperature of any media used to cool the critical component. An arrangement is adapted to utilize these temperature values and information about actual cooling capacity of any cooling equipment present to cool the critical component and information about the thermal behavior of the critical component and the possible cooling media upon a possible change of the power actually transmitted through the station in a mathematical model for calculating the present overload capabilities of the converter station for use in the control of converters of the station upon a possible request of utilizing an overload capability of the station.

1. A converter station connected between an AC system and an HVDC transmission line, said station comprising
 at least one converter having a DC-side thereof connected to a pole of said transmission line on high potential and to low potential and an AC-side connected to said AC system, 
 a plurality of critical components comprising at least one transformer arranged on the AC-side of said converter and converter valves comprising power semiconductor devices, wherein a maximum allowed temperature of said critical components may be reached if power transmitted through the converter station be raised above a rated power of the converter station defined as the maximum power allowed to be transmitted through the converter station at continuous operation and at a maximum ambient temperature, 
 a control device adapted to control said at least one converter for determining a level of power transmitted through the converter station, 
 an overload limiting arrangement adapted to, based upon information about an ambient temperature prevailing, determine an overload capability of the converter station defined as how much more power than said rated power may be transmitted through the station for a certain period of time without exceeding said maximum allowed temperature of said critical components and deliver this information to said control device for being used thereby upon a possible request of utilizing this overload capability, wherein said overload limiting arrangement is adapted to carry out said calculation of overload capabilities for each of said critical components and determine lowest overload capabilities so obtained as the converter station overload capabilities, 
 an element adapted to determine a value of an actual temperature of said critical components, and 
 an element adapted to determine a value of an actual temperature of any media used to cool said critical components, wherein said overload limiting arrangement is adapted to utilize these temperature values as well as information about actual cooling capacity of any cooling equipment present to cool said critical components and information about a thermal behavior of said critical components and said any media used to cool said critical components upon a possible change of power actually transmitted through the station in a mathematical model for calculating present overload capabilities of the converter station for use in control of the control device upon a possible said request. 
 
     
     
       2. The converter station according to  claim 1 , wherein said overload limiting arrangement is adapted to continuously calculate said present overload capabilities. 
     
     
       3. The converter station according to  claim 1 , wherein said overload limiting arrangement is adapted to calculate a continuous overload capability of the converter station defined as how much more power than said rated power may continuously without any restriction of time be transmitted through the station at the conditions prevailing of ambient temperature and cooling capacity of said cooling medium. 
     
     
       4. The converter station according to  claim 1 , wherein said overload limiting arrangement is adapted to calculate a short time overload capability of the converter station defined as how much more power than said rated power may be transmitted through the station for a restricted period of time without exceeding said maximum allowed temperature of said critical components. 
     
     
       5. The converter station according to  claim 4 , wherein said station is designed to connect an AC system to an HVDC bipolar transmission line through two converters, wherein said control device is adapted to utilize information about said short time overload capability of the station calculated for controlling said converter for determining a level of power to be transmitted through the station above said rated power allowed for a certain period of time, upon changing from bipolar operation of the station to monopolar operation thereof. 
     
     
       6. The converter station according to  claim 1 , wherein the element adapted to determine a value of the actual temperature of any media used to cool said critical components comprise an element adapted to measure the temperature of said cooling media. 
     
     
       7. The converter station according to  claim 6 , wherein the element adapted to determine a value of the actual temperature of said critical components are adapted to determine said temperature value by a calculation thereof based upon information about the actual temperature of said cooling media and said cooling capacity of any cooling equipment. 
     
     
       8. The converter station according to  claim 7 , further comprising:
 an element adapted to measure the current through said critical components, wherein said overload limiting arrangement is adapted to base the calculation of the present overload capabilities of the converter station also upon information about the value of said current. 
 
     
     
       9. The converter station according to  claim 8 , wherein said overload limiting arrangement is adapted to base the calculation of the present overload capabilities of the converter station also upon a thermal time constant of said cooling media and/or of said critical components. 
     
     
       10. The converter station according to  claim 1 , wherein said overload limiting arrangement is adapted to use a mathematical model in the form of a thermal model of a relation of a temperature increase of said cooling media versus the current through said critical components for calculating a development of the temperature of said critical components and by that determine a level of power that may be transmitted through the converter station for different periods of time as of the moment of said calculation. 
     
     
       11. The converter station according to  claim 1 , wherein said overload limiting arrangement is adapted to calculate which current through said critical components and by that which power transmitted through the station will give a certain maximum allowed temperature of said critical components within a predetermined period of time. 
     
     
       12. The converter station according to  claim 1 , wherein windings of said at least one transformer are oil-insulated and immersed in a cooling media comprising an oil bath, and wherein said element adapted to determine a value of the actual temperature of any media used to cool said critical components are adapted to measure the temperature of said oil. 
     
     
       13. The converter station according to  claim 1 , wherein said overload limiting arrangement is adapted to base said calculation upon a measurement of the direct current flowing through said converter valves and/or the voltage across said converter valves and/or the temperature of a cooling liquid, used for cooling the valves and/or the control angle of thyristors of the valves when thyristors are used as power semiconductor devices in the valves and/or the overlap angle, during which two parallel valves both are conducting current. 
     
     
       14. The converter station according to  claim 1 , wherein the critical components comprise valve reactors. 
     
     
       15. The converter station according to  claim 14 , wherein said valve reactors are air insulated and cooled by ambient air and said overload limiting arrangement is adapted to utilize results of measurements of the ambient temperature and the current through said reactor for calculating said overload capability of said reactors. 
     
     
       16. The converter station according to  claim 1 , wherein said overload limiting arrangement is adapted to carry out said calculation of said present overload capabilities of the converter station while utilizing data stored in the form of results of a temperature rise test of said critical components with said cooling media and possible cooling equipment, through which both a final temperature rise and a thermal time constant have been determined for said critical components and/or said cooling media. 
     
     
       17. A method for controlling a converter station connected between an AC system and an HVDC transmission line, said station comprising at least one converter having a DC side thereof connected to a pole of said transmission line on high potential and to low potential and an AC side connected to said AC system, said station comprising a plurality of critical components comprising at least one transformer arranged on the AC-side of said converter and converter valves comprising power semiconductor devices, wherein a maximum allowed temperature of said critical components may be reached if power transmitted through the converter station be raised above a rated power of the converter station defined as the maximum power allowed to be transmitted through the converter station at continuous operation and at a maximum ambient temperature, the method comprising:
 controlling said converter for determining the level of power transmitted through the converter station, 
 determining, based upon information about the ambient temperature prevailing, the overload capability of the converter station defined as how much more power than said rated power may be transmitted through the station for a certain period of time without exceeding said maximum allowed temperature of said critical components, wherein said calculation of overload capabilities is carried out for each of said critical components and the lowest overload capabilities so obtained are determined as the converter station overload capabilities, 
 utilizing the information for said control of said converter upon a possible request of utilizing this overload capability, 
 determining a value of the actual temperature of said critical components, 
 determining a value of the actual temperature of any media used to cool said critical components, and 
 utilizing the temperature values and information about actual cooling capacity of any cooling equipment present to cool said critical components and information about the thermal behavior of said critical components and said any media used to cool said critical components upon a possible change of the power actually transmitted through the station in a mathematical model for calculating the present overload capabilities of the converter station for use in said control upon a possible said request. 
 
     
     
       18. The method according to  claim 17 , wherein said present overload capabilities are continuously calculated. 
     
     
       19. The method according to  claim 17 , further comprising:
 calculating a continuous overload capability of the converter station defined as how much more power than said rated power may be continuously without any restriction of time be transmitted through the station at the conditions prevailing of ambient temperature and cooling capacity of said cooling medium. 
 
     
     
       20. The method according to according to  claim 17 , further comprising:
 calculating a short time overload capability of the converter station defined as how much more power than said rated power may be transmitted through the station for a restricted period of time without exceeding said maximum allowed temperature of said critical components. 
 
     
     
       21. The method according to  claim 20 , wherein the method is carried out for a station designed to connect an AC system to an HVDC bipolar transmission line through two converters, the method further comprising:
 utilizing information about said short time overload capability of the station calculated for controlling said converter for determining a level of power to be transmitted through the station above said rated power allowed for a certain period of time, upon changing from bipolar operation of the station to monopolar operation thereof. 
 
     
     
       22. The method according to  claim 17 , wherein a mathematical model in the form of a thermal model of a relation of a temperature increase of said cooling media versus the current through said critical components are used for calculating a development of the temperature of said critical components and by that determine a level of power that may be transmitted through the converter station for different periods of time as of the moment of said calculation. 
     
     
       23. The method according to  claim 17 , further comprising:
 calculating which current through said critical components and by that which power transmitted through the station will give a certain maximum allowed temperature of said critical components within a predetermined period of time. 
 
     
     
       24. The method according to  claim 17 , wherein said calculation of said present overload capabilities of the converter station is carried out while utilizing data stored in the form of results of a temperature rise test of said critical components with said cooling media and possible cooling equipment, through which both a final temperature rise and a thermal time constant have been determined for said critical components and/or said cooling media. 
     
     
       25. A computer program product, comprising:
 a non-transitory computer readable medium; and 
 computer program instructions recorded on the computer readable medium and executable by a processor for carrying out a method for controlling a converter station connected between an AC system and an HVDC transmission line, said station comprising at least one converter having a DC side thereof connected to a pole of said transmission line on high potential and to low potential and an AC side connected to said AC system, said station comprising a plurality of critical components a plurality of critical components comprising at least one transformer arranged on the AC-side of said converter and converter valves comprising power semiconductor devices, wherein a maximum allowed temperature of said critical components may be reached if power transmitted through the converter station be raised above a rated power of the converter station defined as the maximum power allowed to be transmitted through the converter station at continuous operation and at a maximum ambient temperature, the method comprising: 
 controlling said converter for determining the level of power transmitted through the converter station, 
 determining, based upon information about the ambient temperature prevailing, the overload capability of the converter station defined as how much more power than said rated power may be transmitted through the station for a certain period of time without exceeding said maximum allowed temperature of said critical components, wherein said calculation of overload capabilities is carried out for each of said critical components and the lowest overload capabilities so obtained are determined as the converter station overload capabilities, 
 utilizing the information for said control of said converter upon a possible request of utilizing this overload capability, 
 determining a value of the actual temperature of said critical components, 
 determining a value of the actual temperature of any media used to cool said critical components, and 
 utilizing the temperature values and information about actual cooling capacity of any cooling equipment present to cool said critical components and information about the thermal behavior of said critical components and said any media used to cool said critical components upon a possible change of the power actually transmitted through the station in a mathematical model for calculating the present overload capabilities of the converter station for use in said control upon a possible said request. 
 
     
     
       26. The computer program product according to  claim 25 , wherein the computer program instructions are provided at least partially through a network. 
     
     
       27. The computer program product according to  claim 26 , wherein the network is the internet.